The present disclosure relates to emulsion aggregation processes. More specifically, the present disclosure relates to production of emulsion aggregation toner particles via a series of continuous stirred tank reactors (CSTR).
Processes for forming toner compositions for use with electrophotographic print or copy devices have been previously disclosed. For example, methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 7,785,763, 7,749,673, 7,695,884, 7,615,328, 7,429,443, 7,329,476, 6,830,860, 6,803,166, 6,764,802, the disclosures of each of which are hereby incorporated by reference in their entirety.
As noted above, latex polymers utilized in the formation of EA type toners may be formed by batch or semi-continuous emulsion polymerization. Batch processes for producing resins may be subjected to bulk polycondensation polymerization in a batch reactor at an elevated temperature. The time required for the polycondensation reaction is long, due to heat transfer of the bulk material, high viscosity, and limitations on mass transfer. The resulting resin is then cooled, crushed, and milled prior to being dissolved into a solvent. The dissolved resin is then subjected to a phase inversion process where the polyester resin is dispersed in an aqueous phase to prepare polyester latexes. The solvent is then removed from the aqueous phase by a distillation method.
In addition, where a batch process is utilized for aggregation and/or coalescence of latex, because the individual batch process involves the handling of bulk amounts of material and heating of these materials, each process may take many hours to complete before moving to the next process in the formation of the toner particles, that is, aggregation and/or coalescence. In addition, batch-to-batch consistency is frequently difficult to achieve because of variations that may arise from one batch to another.
Moreover, methods of improving the space time yield of the EA process have been previously examined, but without yielding particles of interest. For example, continuous tubular reactors have been studied, but some issues remain with respect to their use at producing toner particles.
Small-sized toner particles are difficult to produce in batch because the smaller particulate size can increase emulsion viscosity, which can confound stirring efficiency, resulting in variable particle size.
Therefore, other reactors for the preparation of toner particles, such as, small-sized toner particles in a continuous process are desirable. Such reactors should be more efficient, take less time, result in a consistent toner particle product, and be environmentally friendly.